WO2015074529A1 - Sub-module capacitor voltage balancing optimization method for modular multilevel converter - Google Patents

Sub-module capacitor voltage balancing optimization method for modular multilevel converter Download PDF

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WO2015074529A1
WO2015074529A1 PCT/CN2014/091351 CN2014091351W WO2015074529A1 WO 2015074529 A1 WO2015074529 A1 WO 2015074529A1 CN 2014091351 W CN2014091351 W CN 2014091351W WO 2015074529 A1 WO2015074529 A1 WO 2015074529A1
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sub
module
capacitor voltage
information
solution
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PCT/CN2014/091351
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French (fr)
Chinese (zh)
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姜喜瑞
谢敏华
王韧秋
高阳
杨岳峰
贺之渊
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国家电网公司
国网智能电网研究院
中电普瑞电力工程有限公司
国网辽宁省电力有限公司大连供电公司
华北电网有限公司
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Publication of WO2015074529A1 publication Critical patent/WO2015074529A1/en

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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
    • H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
    • H02M7/44—Conversion of dc power input into ac power output without possibility of reversal by static converters
    • H02M7/48—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M7/483—Converters with outputs that each can have more than two voltages levels
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
    • H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
    • H02M7/44—Conversion of dc power input into ac power output without possibility of reversal by static converters
    • H02M7/48—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M7/483—Converters with outputs that each can have more than two voltages levels
    • H02M7/4835—Converters with outputs that each can have more than two voltages levels comprising two or more cells, each including a switchable capacitor, the capacitors having a nominal charge voltage which corresponds to a given fraction of the input voltage, and the capacitors being selectively connected in series to determine the instantaneous output voltage

Definitions

  • the invention relates to a balance optimization algorithm in the field of power electronic direct current transmission of a power system, in particular to a sub-module capacitor voltage balance optimization method of a modular multi-level converter.
  • the converter valve When multi-modular multi-level (MMC) technology is applied in the field of high-voltage direct current transmission, the converter valve needs hundreds or even thousands of sub-modules in series, and each sub-module must be controlled separately; the sub-module storage capacitors are independent of each other due to the material. And the manufacturing level limit, capacitance capacity, equivalent series internal resistance, self-discharge rate and temperature distribution, etc., all have certain dispersion, and also consider the energy pulsation, power fluctuation and loss in the bridge arm. During discharge, energy exchange and operation, the sub-module capacitor voltage will be unbalanced; and the proper resolution of the voltage equalization problem directly determines the output performance of the inverter. Therefore, the sub-module capacitor voltage balance algorithm is the whole. The premise and basis of whether the flexible DC transmission system can operate stably.
  • the capacitor level modulation method and its optimization method (to ensure that the switching frequency of the device is minimized when the voltage distortion rate is not too large) is the main way for the flexible DC transmission system to balance the modulation of the sub-module capacitor voltage.
  • the maximum value is the power frequency sine wave with the number of input modules and the minimum value of zero as the modulation wave of the nearest level.
  • the sub-module voltage is tracked in real time, and the whole sub-cycle is sorted to determine the decision of the switching sub-module;
  • small such as the flexible wind power transmission demonstration project of Shanghai Wind Farm, the engineering scale is 20MW, the maximum input of the module is 49, the number of steps of the power frequency sine wave step wave is 50
  • 200Us data acquisition capability, data processing capability, algorithm implementation control ability and channel delay and reliability caused by system hardware
  • the requirements of transmission and other aspects are completely satisfactory; however, as the scale of the project increases dramatically, the maximum number of inputs of the module will reach 200 to 400 or more, the corresponding number of steps of the power frequency sine wave will also reach 200 to 400 or more.
  • the Tabu Search algorithm is an intelligent heuristic search optimization algorithm with flexible memory function. It avoids repeated search by introducing flexible storage structure and corresponding taboo criteria, and exempts some excellent states in the taboo table through special guidelines. Furthermore, the algorithm can search for the global optimal solution of the multi-extreme point objective function; the tabu search algorithm has been deeply studied in various fields such as unit load distribution of power system, fault recovery and reconstruction of distribution network, and reactive power optimization. Application, but based on the tabu search optimization algorithm, the flexible base-transmission system valve-based control strategy is rarely studied and applied at home and abroad.
  • the object of the present invention is to provide a sub-module capacitor voltage balance optimization method for a modular multi-level converter, which is controlled by a distributed parallel processing method for a flexible DC transmission system.
  • the architecture, the decision-predicting implementation of the modulation and balance algorithm of the sub-module capacitor voltage, The current direction, the number of modulation inputs, the sub-module voltage, the sub-module state, and the device switching frequency are the key parameters of the algorithm.
  • the sub-modules of the switching action are pre-decisive, and the whole
  • the key factors such as the current, DC voltage and bridge arm current change rate of the three-phase upper and lower arms are added to the algorithm, and the microsecond-level periodic decision is converted into a millisecond-level periodic batch decision, and a set of global optimal solutions is quickly searched.
  • the method of the overall prediction sub-module capacitor voltage balance modulation algorithm of the valve-based control algorithm of the flexible direct current transmission system is realized, thereby achieving the system regulation requirement.
  • the invention provides a sub-module capacitor voltage balance optimization method for a modular multi-level converter.
  • the system for the method is a modular multi-level commutation system, and a flexible DC based on distributed parallel processing is established.
  • the transmission system valve-based control architecture is improved in that the method comprises the following steps:
  • control objectives of the sub-module capacitor voltage balance control include:
  • Capacitance imbalance ⁇ a direct control target for capacitor voltage balance
  • the sub-module capacitor voltage fluctuates within the range of Umax and Umin.
  • step (2) establishing a sub-module state decision optimization model based on the tabu search includes the following steps:
  • ⁇ 1> Establishing a quintuple; a five-tuple composed of five key information of a sub-module and an inverter, the quintuple being the basis of an objective function of a sub-module state decision optimization model, wherein the quintuple is as follows
  • the expression says:
  • U i ; i b ; t k ; K SM ; W is the five key information of the sub-module and the inverter, respectively: U i is the sub-module voltage magnitude, i b is the bridge arm current magnitude and direction information, t k is the sub-module switch action time scale, K SM is the sub-module information state, and W is the total energy of the bridge arm;
  • ⁇ 1 , ⁇ 2 are weight coefficients; ⁇ is the sub-module switching cost; ⁇ is the energy volatility; ⁇ is the sub-module information state;
  • the submodule information state ⁇ is expressed as:
  • the submodule switching cost ⁇ consists of the following two parts:
  • ⁇ 1 , ⁇ 2 are weight coefficients;
  • U ave represents the average value of the sub-module capacitance voltage;
  • the energy fluctuation rate ⁇ is expressed by the following formula.
  • the constraints of the submodule state decision optimization model include:
  • the variability is less than the upper limit
  • Control constraint The sub-module does not perform repeated switching within a single control cycle.
  • the taboo table includes the size of the taboo table, and the scale of the taboo table refers to the maximum number of movements allowed to exist, and the square of the number of submodules is multiplied by 8 to indicate the taboo table.
  • the update uses the "first in, first out" rule;
  • the determining the taboo table includes the following steps:
  • the constraint condition, the control protection unit and the commutation suppression unit determine the number of periodic sub-module inputs, and search for the target value of the calculation unit sub-module in the distributed parallel computing system through the balance optimization algorithm, and find the reach a set of local optimal solutions of conditions;
  • the balance optimization algorithm based on the tabu search is used to balance and optimize the capacitor voltage of the sub-module, including the following steps:
  • system parameters include distributed system operating parameters and parameters required by the algorithm and key calculation factors
  • initial solution of the search this is the initial content, that is, preset a relatively low value
  • step 8 cross-operation, and determine whether the selected solution meets the taboo requirements, if yes, proceed to step 9; otherwise, the selected solution is deleted from the field, and returns to step 5;
  • the system parameters include the current direction of the modular multi-level commutation system sub-module, the number of modulation input and output sub-modules, the sub-module voltage level, the sub-module status, and the IGBT device switch in the sub-module. Frequency, current of three-phase upper and lower arms, DC voltage and bridge arm current rate of change.
  • step (4) the on-line simulation and the physical offline simulation test are used to verify the sub-module capacitance voltage balance optimization.
  • tabu search optimization algorithm flexible memory function, flexible storage structure and corresponding tabu criteria to avoid repeated search, and exempt the excellent state in some taboo tables by special criteria, thus ensuring that the algorithm can search for multi-extreme point objective function Global optimal solution;
  • the experimental verification method carried out by the algorithm is a method of verifying the algorithm together with the simulation mode and the dynamic simulation test mode. It is a comprehensive system test method for all the algorithms of the valve-based control technology of high-voltage and large-capacity flexible direct current transmission.
  • FIG. 1 is a topological structural view of a modular multilevel converter provided by the present invention
  • FIG. 2 is a topological structural diagram of a modular multilevel converter submodule provided by the present invention.
  • FIG. 3 is a waveform diagram of a capacitor voltage fluctuation range of a sub-module provided by the present invention.
  • FIG. 4 is a flow chart of a tabu search optimization algorithm for sub-module capacitor voltage balance optimization provided by the present invention
  • FIG. 5 is a schematic structural diagram of a simulation circuit provided by the present invention.
  • FIG. 6 is a waveform diagram of a test mode of a valve base control system of a recent level modulation method
  • FIG. 7 is a voltage waveform diagram of a partial sub-module of a valve-based control system of a recent level modulation method
  • Figure 8 is a frequency waveform diagram of a single switch of a valve-based control system of a recent level modulation method
  • FIG. 9 is a schematic diagram of a test AC waveform of a valve-based control system based on the tabu search optimization algorithm provided by the present invention.
  • FIG. 10 is a voltage waveform diagram of a partial sub-module of a valve-based control system based on the tabu search optimization algorithm provided by the present invention
  • FIG. 11 is a frequency waveform diagram of a single switch of a valve-based control system based on the tabu search optimization algorithm provided by the present invention.
  • FIG. 12 is a flow chart of a sub-module capacitor voltage balance optimization method of a modular multi-level converter provided by the present invention.
  • the invention provides a sub-module capacitor voltage balance optimization method for a modular multi-level converter, wherein the system uses the modular multi-level commutation system and is implemented by a modular multi-level converter.
  • the modular multilevel converter consists of three phases of six bridge arms, each of which is composed of sub-modules cascaded; the sub-modules include insulated gate bipolar power transistors IGBT1 and IGBT2, thyristor V, and storage capacitor C , vacuum switch, a resistor R1 and a resistor R2; the resistor R1 and the resistor R2 are connected in series to form a R1-R2 branch; the vacuum switch, the thyristor V and the IGBT 2 are connected in parallel; the IGBT1 and the IGBT2 are upper and lower structures and the emitter of the IGBT1 is connected to the IGBT2 Collector; the IGBT1, R1-R2 branch and the storage capacitor C are sequentially connected in parallel; the topology structure diagram of the modular multilevel converter
  • Each sub-module includes two upper and lower full-control power electronic devices IGBT1 and IGBT2, a storage capacitor C and a thyristor V that functions as an overcurrent protection function, and a vacuum switch that can be closed by a serious failure of the sub-module.
  • the sub-module is bypassed from the main circuit; the sub-module output capacitor voltage (input) or non-output voltage (exit) can be controlled by controlling the on-off of the internal IGBT of each sub-module, so that each phase of the upper and lower bridge arms always inputs a certain amount.
  • the sub-module can obtain the required DC-side voltage, and at the same time, the AC output voltage of the inverter can be obtained by adjusting the number of sub-modules input by the upper and lower arms.
  • the topology diagram of the submodule is shown in Figure 2.
  • the sub-module capacitor voltage balance optimization method of the modular multi-level converter provided by the present invention has a flow chart as shown in FIG. 12, and includes the following steps:
  • the control target of the sub-module capacitor voltage balance control includes the following aspects:
  • Capacitor overall fluctuation coefficient ⁇ is the overall control target. During the operation of the system, the capacitance voltage fluctuation coefficient of each sub-module meets the design requirements. This performance is related to various factors such as system transmission power, number of redundant sub-modules, capacitance value, commutation control algorithm, and voltage equalization strategy. Comprehensive control objectives.
  • Capacitance unbalance ⁇ a direct control target for capacitor voltage balance. During the system operation, the capacitor voltage balance of each sub-module in each bridge arm is consistent at the same time, which is the direct target of the capacitor voltage balance control. As shown in Figure 3;
  • the sub-module capacitor voltage has ⁇ 8% fluctuation under full power transmission.
  • the limit fluctuation coefficient is ⁇ 15% considering factors such as DC voltage fluctuation, equipment manufacturing tolerance, measurement error, control error, and capacitor voltage balance control error.
  • the capacitance imbalance ⁇ is expressed by the following expression:
  • the sub-module capacitor voltage fluctuates within the range of Umax and Umin.
  • Switching frequency of the device The important obstacle to the development of VSC-HVDC technology is the large loss of the converter. Lowering the switching frequency of the power electronic device can greatly reduce the converter loss; the switching frequency of the device is higher, and the sub-module is switched. More frequent, it will cause a large switching loss, therefore, the switching frequency of the device is an important evaluation index of the voltage balancing algorithm;
  • the difficulty level of the algorithm implementation is related to the architecture, hardware processing capability and software complexity, and also needs to be used as the evaluation index of the voltage balance algorithm.
  • ⁇ 1> Establishing a quintuple; establishing the sub-module state decision-making optimization model based on the tabu search optimization algorithm is the determination of the objective function, and the quintuple composed of the sub-module and the five key information of the whole system is the basis of the objective function.
  • the quintuple is represented by the following expression:
  • U i ; i b ; t k ; K SM ; W is the five key information of the sub-module and the inverter, respectively: U i is the sub-module voltage magnitude, i b is the bridge arm current magnitude and direction information, t k is the sub-module switch action time scale, K SM is the sub-module information state, and W is the total energy of the bridge arm;
  • the objective function is represented by the following expression:
  • ⁇ 1 , ⁇ 2 are weight coefficients; ⁇ is the sub-module switching cost; ⁇ is the energy volatility; ⁇ is the sub-module information state;
  • the submodule information state ⁇ is expressed as:
  • the submodule switching cost ⁇ consists of the following two parts:
  • ⁇ 1 , ⁇ 2 are weight coefficients;
  • U ave represents the average value of the sub-module capacitance voltage;
  • the energy fluctuation rate ⁇ is expressed by the following formula.
  • the constraints of the submodule state decision optimization model include:
  • the variability is less than the upper limit
  • Control constraint The sub-module does not perform repeated switching within a single control cycle.
  • the model uses a domain solution consisting of a centralized solution and a decentralized solution.
  • This method uses sub-module key information - sub-module voltage magnitude, bridge arm current direction, switching action time scale, sub-module
  • the information state and the target value generated by the quintuple of the total energy are accurately moved left and right, and a new solution is randomly generated in the ring where the quintuple is located. This solution is the scatter solution.
  • the termination criterion uses the optimal solution to continuously burst out the constant maximum number of iterations.
  • the taboo table is the key to the taboo algorithm.
  • the maximum number of movements allowed in the taboo table is called the size of the taboo table.
  • the size of the taboo table in the model is multiplied by 8 in the square of the number of submodules, and the traditional “first in, first out” rule is used to update the taboo table.
  • the reason why the release criterion appears in the search algorithm is because the taboo table may limit some "movements" that can lead to the best solution.
  • the model is established using a "release criterion" based on the fitness value: if a movement is applied to the current solution and an optimum adaptation value is reached so far, the movement is considered to satisfy the "release criterion".
  • Determining the taboo table includes the following steps:
  • the constraint condition determines the number of periodic sub-module inputs, and search for the sub-module information target value of the computing unit in the distributed parallel computing system through the balance optimization algorithm, and find a set of local optimal solutions that meet the condition;
  • Integrating a local optimal solution searching for a set of global optimal solutions therein, as a pre-casting sub-module object for switching in each period of the next period;
  • FIG. 4 the flow chart of the tabu search optimization algorithm for the sub-module capacitor voltage balance optimization provided by the present invention is shown in FIG. 4, and includes the following steps:
  • system parameters include distributed system operating parameters and parameters required by the algorithm and key calculation factors
  • initial solution of the search this is the initial content, that is, preset a relatively low value
  • step 8 cross-operation, and determine whether the selected solution meets the taboo requirements, if yes, proceed to step 9; otherwise, the selected solution is deleted from the field, and returns to step 5;
  • the PSCAD/EMTDC simulation software and the dynamic simulation test device are used to build the system model of the valve-based control system of the nearest level approximation modulation strategy and the tabu search optimization algorithm.
  • the PSCAD/EMTDC simulation software builds a single-site three-phase passive inverter circuit with limit parameters, as shown in Figure 5; the dynamic simulation test platform builds a single-phase passive inverter test with limit parameters; through the comparative analysis of the test, the tabu search is obtained.
  • the optimization algorithm is superior to the nearest level approximation modulation strategy in the evaluation index.
  • valve-based control system of the current level modulation method and the voltage waveform of some sub-modules and the frequency waveform of a single switch are shown in Figure 6-8.
  • the valve-based control system based on the tabu search optimization algorithm tests the AC waveform and the voltage waveform of some sub-modules and the frequency of a single switch as shown in Figure 9-11.
  • the summary of the test results comparison table is shown in Table 1:

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Abstract

Disclosed is a sub-module capacitor voltage balancing optimization method for a modular multilevel converter. The system used in the method is a modular multilevel converter system, and a flexible direct current power transmission system valve based control system architecture using a distributed parallel processing mode as the architecture is established. The method comprises the following steps: (1) determining the objective of sub-module capacitior voltage balancing control; (2) establishing a sub-module state decision optimization model; (3) performing sub-module capacitor voltage balancing optimization; and (4) verifying the sub-module capacitior voltage balancing optimization. The adoption of the distributed computation architecture results in a great improvement of processing capability, and also guarantees the application of complex algorithm strategies in high-voltage large-capacity flexible direct current power transmission system.

Description

一种模块化多电平换流器的子模块电容电压平衡优化方法Sub-module capacitor voltage balance optimization method for modular multilevel converter 技术领域Technical field
本发明涉及一种电力系统的电力电子直流输电领域的平衡优化算法，具体涉及一种模块化多电平换流器的子模块电容电压平衡优化方法。The invention relates to a balance optimization algorithm in the field of power electronic direct current transmission of a power system, in particular to a sub-module capacitor voltage balance optimization method of a modular multi-level converter.
背景技术Background technique
模块化多电平(MMC)技术在高压直流输电领域应用时，换流阀需要数百乃至数千只子模块串联，而每个子模块都必须单独控制；子模块储能电容彼此独立，由于材料和制造水平的限制，电容容量、等效串联内阻、自放电速率以及温度分布等参数，都具有一定的离散性，另外考虑到桥臂内能量脉动、功率脉动的变化以及损耗方面，在充放电、能量交换以及运行过程中，子模块电容电压会产生不平衡的状况；而均压问题的妥善解决与否直接决定换流器输出性能的优劣，因此，子模块电容电压平衡算法是整个柔性直流输电系统是否能够稳定运行的前提和基础。When multi-modular multi-level (MMC) technology is applied in the field of high-voltage direct current transmission, the converter valve needs hundreds or even thousands of sub-modules in series, and each sub-module must be controlled separately; the sub-module storage capacitors are independent of each other due to the material. And the manufacturing level limit, capacitance capacity, equivalent series internal resistance, self-discharge rate and temperature distribution, etc., all have certain dispersion, and also consider the energy pulsation, power fluctuation and loss in the bridge arm. During discharge, energy exchange and operation, the sub-module capacitor voltage will be unbalanced; and the proper resolution of the voltage equalization problem directly determines the output performance of the inverter. Therefore, the sub-module capacitor voltage balance algorithm is the whole. The premise and basis of whether the flexible DC transmission system can operate stably.
当前，电容电平调制法及其优化方法(保证电压畸变率不太大的情况下，尽量降低器件的开关频率)是柔性直流输电系统对子模块电容电压进行平衡调制的主要方式，此方式以最大值为投入模块数、最小值为零的工频正弦波作为最近电平的调制波，通过实时跟踪子模块电容电压，并通过每周期整体排序，确定投切子模块决策；在建设工程的规模不大的情况下(如上海风电场柔性直流输电示范工程，工程规模20MW，模块最大投入数是49，工频正弦波阶梯波的台阶数为50)，对于控制保护系统和阀基控制算法来讲，以200us(工频20ms，半周期50个台阶，控制周期10ms/50＝200Us)为操作周期，其数据采集能力、数据处理能力、算法实现控制能力以及系统硬件引起的通道延时和可靠传输等方面要求，是完全可以满足的；但是，随着工程规模的剧增，其模块最大投入数将达到200到400以上，相应的工频正弦波的台阶数也将达到200到400以上，若还是按照原有的实时控制决策方式的控制策略，将需要以低于50Us的周期处理时间，对于系统的采集能力和通道延时及可靠传输等要求，规模将是成倍的，数据处理能力和算法实现控制能力要求则成指数倍的；因此，对于以实时采集、实时控制方式为主的算法平衡实现，将变得非常困难。At present, the capacitor level modulation method and its optimization method (to ensure that the switching frequency of the device is minimized when the voltage distortion rate is not too large) is the main way for the flexible DC transmission system to balance the modulation of the sub-module capacitor voltage. The maximum value is the power frequency sine wave with the number of input modules and the minimum value of zero as the modulation wave of the nearest level. The sub-module voltage is tracked in real time, and the whole sub-cycle is sorted to determine the decision of the switching sub-module; In the case of small (such as the flexible wind power transmission demonstration project of Shanghai Wind Farm, the engineering scale is 20MW, the maximum input of the module is 49, the number of steps of the power frequency sine wave step wave is 50), for the control protection system and the valve base control algorithm Speaking, with 200us (power frequency 20ms, half cycle 50 steps, control cycle 10ms/50=200Us) as the operation cycle, its data acquisition capability, data processing capability, algorithm implementation control ability and channel delay and reliability caused by system hardware The requirements of transmission and other aspects are completely satisfactory; however, as the scale of the project increases dramatically, the maximum number of inputs of the module will reach 200 to 400 or more, the corresponding number of steps of the power frequency sine wave will also reach 200 to 400 or more. If it is still in accordance with the original real-time control decision-making control strategy, it will need to process the time in less than 50Us for the system. The requirements of acquisition capability, channel delay and reliable transmission will be doubled, and the data processing capability and algorithm implementation control requirements will be exponentially multiplied; therefore, the algorithm based on real-time acquisition and real-time control is balanced. Will become very difficult.
禁忌(Tabu Search)算法是一种智能启发式搜索优化算法，具有灵活的记忆功能，通过引入灵活的存储结构和相应的禁忌准则避免重复搜索，并通过特赦准则赦免一些禁忌表中的优良状态，进而保证算法能够搜索到多极值点目标函数的全局最优解；禁忌搜索算法在电力系统的机组负荷分配、配电网故障恢复重构、无功优化等多种领域得到了深入的研究和应用，但基于禁忌搜索优化算法的柔性直流输电系统阀基控制策略方面，国内外很少研究和应用。The Tabu Search algorithm is an intelligent heuristic search optimization algorithm with flexible memory function. It avoids repeated search by introducing flexible storage structure and corresponding taboo criteria, and exempts some excellent states in the taboo table through special guidelines. Furthermore, the algorithm can search for the global optimal solution of the multi-extreme point objective function; the tabu search algorithm has been deeply studied in various fields such as unit load distribution of power system, fault recovery and reconstruction of distribution network, and reactive power optimization. Application, but based on the tabu search optimization algorithm, the flexible base-transmission system valve-based control strategy is rarely studied and applied at home and abroad.
发明内容Summary of the invention
针对现有技术的不足，本发明的目的是提供一种模块化多电平换流器的子模块电容电压平衡优化方法，该方法以分布式并行处理方式为架构的柔性直流输电系统阀基控制体系架构，对子模块电容电压的调制和平衡算法作决策预测实现， 以电流方向、调制投入切出个数、子模块电压大小、子模块状态、器件开关频率等作为算法实现的关键参数，通过禁忌搜索优化算法，对开关动作的子模块进行预先决策，并从整体上将三相上下桥臂的电流、直流电压、桥臂电流变化率等关键因素加入到算法中，将微秒级周期决策转化为毫秒级周期批处理决策，快速搜索一组全局最优解，作为下一周期的子模块投切对象，以此实现柔性直流输电系统阀基控制算法的整体预测子模块电容电压平衡调制算法的方式，从而达到系统调控的要求。In view of the deficiencies of the prior art, the object of the present invention is to provide a sub-module capacitor voltage balance optimization method for a modular multi-level converter, which is controlled by a distributed parallel processing method for a flexible DC transmission system. The architecture, the decision-predicting implementation of the modulation and balance algorithm of the sub-module capacitor voltage, The current direction, the number of modulation inputs, the sub-module voltage, the sub-module state, and the device switching frequency are the key parameters of the algorithm. Through the tabu search optimization algorithm, the sub-modules of the switching action are pre-decisive, and the whole The key factors such as the current, DC voltage and bridge arm current change rate of the three-phase upper and lower arms are added to the algorithm, and the microsecond-level periodic decision is converted into a millisecond-level periodic batch decision, and a set of global optimal solutions is quickly searched. As the sub-module switching object of the next cycle, the method of the overall prediction sub-module capacitor voltage balance modulation algorithm of the valve-based control algorithm of the flexible direct current transmission system is realized, thereby achieving the system regulation requirement.
本发明的目的是采用下述技术方案实现的：The object of the present invention is achieved by the following technical solutions:
本发明提供一种模块化多电平换流器的子模块电容电压平衡优化方法，所述方法用的系统为模块化多电平换流系统，建立以分布式并行处理方式为架构的柔性直流输电系统阀基控制体系架构，其改进之处在于，所述方法包括下述步骤：The invention provides a sub-module capacitor voltage balance optimization method for a modular multi-level converter. The system for the method is a modular multi-level commutation system, and a flexible DC based on distributed parallel processing is established. The transmission system valve-based control architecture is improved in that the method comprises the following steps:
(1)确定子模块电容电压平衡控制的控制目标；(1) determining a control target of the sub-module capacitance voltage balance control;
(2)建立子模块状态决策优化模型；(2) Establish a sub-module state decision optimization model;
(3)对子模块电容电压进行平衡优化；(3) Balance and optimize the capacitor voltage of the sub-module;
(4)对子模块电容电压平衡优化进行验证。(4) Verify the sub-module capacitor voltage balance optimization.
进一步地，所述步骤(1)中，子模块电容电压平衡控制的控制目标包括：Further, in the step (1), the control objectives of the sub-module capacitor voltage balance control include:
1)电容总体波动系数δ：为总体控制目标；1) The overall fluctuation coefficient of capacitance δ: the overall control target;
2)电容不平衡度ε：为电容电压平衡的直接控制目标；2) Capacitance imbalance ε: a direct control target for capacitor voltage balance;
3)器件的开关频率；3) the switching frequency of the device;
4)平衡优化算法的实现难易。4) The implementation of the balance optimization algorithm is difficult.
进一步地，所述电容不平衡度ε用下述表达式表示：Further, the capacitance imbalance ε is expressed by the following expression:
Figure PCTCN2014091351-appb-000001
     式1>；
Figure PCTCN2014091351-appb-000001
 Formula 1>;
其中，
Figure PCTCN2014091351-appb-000002
使子模块电容电压在Umax和Umin范围内波动。among them,
Figure PCTCN2014091351-appb-000002
The sub-module capacitor voltage fluctuates within the range of Umax and Umin.
进一步地，所述步骤(2)中，建立基于禁忌搜索的子模块状态决策优化模型包括下述步骤：Further, in the step (2), establishing a sub-module state decision optimization model based on the tabu search includes the following steps:
<1>建立五元组；子模块及换流器的五个关键信息构成的五元组，所述五元组是子模块状态决策优化模型目标函数的基础，所述五元组用下述表达式表示：<1> Establishing a quintuple; a five-tuple composed of five key information of a sub-module and an inverter, the quintuple being the basis of an objective function of a sub-module state decision optimization model, wherein the quintuple is as follows The expression says:
B＝{Ui；ib；tk；KSM；W}     式2>；B={U i ; i b ; t k ; K SM ; W} Equation 2>;
其中，Ui；ib；tk；KSM；W为子模块及换流器的五个关键信息，分别为：Ui为子模块电压大小，ib为桥臂电流大小及方向信息，tk为子模块开关动作时标，KSM为子模块信息状态，W为桥臂总能量；Among them, U i ; i b ; t k ; K SM ; W is the five key information of the sub-module and the inverter, respectively: U i is the sub-module voltage magnitude, i b is the bridge arm current magnitude and direction information, t k is the sub-module switch action time scale, K SM is the sub-module information state, and W is the total energy of the bridge arm;
<2>确定目标函数和约束条件；<2> Determine the objective function and constraints;
<3>确定禁忌表。 <3> Determine the taboo table.
进一步地，所述子模块状态决策优化模型的目标函数用下述表达式表示：Further, the objective function of the sub-module state decision optimization model is represented by the following expression:
Figure PCTCN2014091351-appb-000003
     式3>；
Figure PCTCN2014091351-appb-000003
 Equation 3>;
其中：α1，α2均为权重系数；η为子模块投切代价；φ为能量波动率；β为子模块信息状态；Where: α 1 , α 2 are weight coefficients; η is the sub-module switching cost; φ is the energy volatility; β is the sub-module information state;
子模块信息状态β表示为：The submodule information state β is expressed as:
Figure PCTCN2014091351-appb-000004
Figure PCTCN2014091351-appb-000004
子模块投切代价η由以下两部分组成：The submodule switching cost η consists of the following two parts:
Figure PCTCN2014091351-appb-000005
     式5>；
Figure PCTCN2014091351-appb-000005
 Equation 5>;
其中，γ1，γ2均为权重系数；Uave表示子模块电容电压平均值；Where γ 1 , γ 2 are weight coefficients; U ave represents the average value of the sub-module capacitance voltage;
能量波动率φ由下式表示，The energy fluctuation rate φ is expressed by the following formula.
Figure PCTCN2014091351-appb-000006
     式6>；
Figure PCTCN2014091351-appb-000006
 Equation 6>;
其中，ci和ui分别为各子模块电容和电压；i＝1,2,…n；n表示子模块个数；CN表示桥臂整个电容的电容值，UN表示整个桥臂的电压值；Where c i and u i are the capacitance and voltage of each sub-module respectively; i=1, 2,...n; n represents the number of sub-modules; C N represents the capacitance value of the entire capacitor of the bridge arm, and U N represents the entire bridge arm Voltage value;
子模块状态决策优化模型的约束条件包括：The constraints of the submodule state decision optimization model include:
A、总电压约束：Umin＜Σu＜Umax，总体电压不能超过上限和下限；A, the total voltage constraint: U min < Σ u < U max , the overall voltage can not exceed the upper and lower limits;
B、子模块电压畸变约束：
Figure PCTCN2014091351-appb-000007
子模块电压畸B, sub-module voltage distortion constraints:
Figure PCTCN2014091351-appb-000007
Submodule voltage distortion
变率小于上限值；The variability is less than the upper limit;
C、电气极限约束：过电流控制，用于保证桥臂电流值在允许限值内；桥臂电流值根据直流系统容量确定，1000WM，±320kV直流系统电流值在1600A±10％范围内；C. Electrical limit constraint: Overcurrent control is used to ensure that the bridge arm current value is within the allowable limit; the bridge arm current value is determined according to the DC system capacity, 1000WM, ±320kV DC system current value is in the range of 1600A ± 10%;
D、控制约束：子模块在单控制周期内不进行重复投切。 D. Control constraint: The sub-module does not perform repeated switching within a single control cycle.
进一步地，所述步骤<3>中，禁忌表包括禁忌表的规模，禁忌表的规模指的是允许存在的最大移动数目称，采用子模块数目的开平方数乘以8表示，对禁忌表的更新采用“先入先出”规则；Further, in the step <3>, the taboo table includes the size of the taboo table, and the scale of the taboo table refers to the maximum number of movements allowed to exist, and the square of the number of submodules is multiplied by 8 to indicate the taboo table. The update uses the "first in, first out" rule;
所述确定禁忌表包括下述步骤：The determining the taboo table includes the following steps:
a、通过分布式架构的信息共享协议机制将周期内各并行计算单元的子模块信息进行收集，形成五元组信息树进行保存，并计算其目标值；a. collecting the sub-module information of each parallel computing unit in the cycle through the information sharing protocol mechanism of the distributed architecture, forming a quintuple information tree for saving, and calculating the target value thereof;
b、根据目标函数、约束条件、控制保护单元和换流抑制单元确定的周期子模块投入数，并通过平衡优化算法对分布式并行计算系统中的计算单元子模块信息目标值进行搜索，找到达到条件的一组局部最优解；b. According to the objective function, the constraint condition, the control protection unit and the commutation suppression unit, determine the number of periodic sub-module inputs, and search for the target value of the calculation unit sub-module in the distributed parallel computing system through the balance optimization algorithm, and find the reach a set of local optimal solutions of conditions;
c、综合局部最优解，在其中搜索一组全局最优解，作为下一周期各时段进行投切的预投切子模块对象；c. Integrating a local optimal solution, searching for a set of global optimal solutions therein, as a pre-casting sub-module object for switching in each period of the next period;
d、确定每个预投切子模块的投切时间点和顺序，确保下一周期的子模块投切决策，将相关信息发送执行单元，相关信息指的是需要投切的子模块序号及系统的控制保护信息。d. Determine the switching time point and sequence of each pre-cast sub-module, ensure the sub-module switching decision of the next cycle, and send relevant information to the execution unit, and the related information refers to the sub-module serial number and system that need to be switched. Control protection information.
进一步地，所述步骤(3)中，采用基于禁忌搜索的平衡优化算法对子模块电容电压进行平衡优化，包括下述步骤：Further, in the step (3), the balance optimization algorithm based on the tabu search is used to balance and optimize the capacitor voltage of the sub-module, including the following steps:
①读入系统参数(系统参数包括分布式系统运行参数和算法所需的参量和关键计算因子)，确定搜索的起始解(此为初始化的内容，即预设一个相对低值)；1 reading in the system parameters (system parameters include distributed system operating parameters and parameters required by the algorithm and key calculation factors), determine the initial solution of the search (this is the initial content, that is, preset a relatively low value);
②读入子模块五元组信息，形成初始化信息群；2 reading the sub-module quintuple information to form an initialization information group;
③确定禁忌长度，禁忌表长度，并将禁忌表置空；(禁忌长度是指需要搜索的信息数量，而禁忌表的长度则是搜索到的值的数量)3 Determine the length of the taboo, the length of the taboo table, and set the taboo table; (taboo length refers to the amount of information to be searched, and the length of the taboo table is the number of values searched)
④确定周期内需调整的时段：通过周期长度和预设精度来进行调整，即确定周期内投切子模块数目和投切间隔；4 determining the period to be adjusted within the period: adjusting by the period length and the preset precision, that is, determining the number of switching sub-modules and the switching interval in the period;
⑤生成当前解的领域：通过五元组的信息树，搜索相邻叶子和节点，生成解邻域；5 Generating the domain of the current solution: searching for adjacent leaves and nodes through the information tree of the quintuple to generate a solution neighborhood;
⑥从领域中选择目标函数最优的解，即候选解；6 Selecting the optimal solution of the objective function from the domain, ie the candidate solution;
⑦取适应度相对最优的候选解；7 taking a candidate solution with relatively optimal fitness;
⑧进行交叉操作，并判断选中解是否满足禁忌要求，若满足，则进行步骤⑨；否则将选中解从领域中删除，并返回步骤⑤；8 cross-operation, and determine whether the selected solution meets the taboo requirements, if yes, proceed to step 9; otherwise, the selected solution is deleted from the field, and returns to step 5;
⑨将选中的解作为新的当前解；9 will use the selected solution as the new current solution;
⑩判断是否超过最大迭代次数，若已达到，则得到最优解；否则，更新禁忌表，并对当前解进行适应度计算，返回步骤⑤。10 determines whether the maximum number of iterations is exceeded. If it has been reached, the optimal solution is obtained; otherwise, the taboo table is updated, and the fitness solution is calculated for the current solution, and the process returns to step 5.
进一步地，所述步骤①中，系统参数包括模块化多电平换流系统子模块的电流方向、调制投入切出子模块个数、子模块电压大小、子模块状态、子模块中IGBT器件开关频率、三相上下桥臂的电流、直流电压和桥臂电流变化率。Further, in the step 1, the system parameters include the current direction of the modular multi-level commutation system sub-module, the number of modulation input and output sub-modules, the sub-module voltage level, the sub-module status, and the IGBT device switch in the sub-module. Frequency, current of three-phase upper and lower arms, DC voltage and bridge arm current rate of change.
进一步地，所述步骤(4)中，采用在线仿真和物理离线仿真试验对子模块电容电压平衡优化进行验证。Further, in the step (4), the on-line simulation and the physical offline simulation test are used to verify the sub-module capacitance voltage balance optimization.
与现有技术比，本发明的有益效果是： Compared with the prior art, the beneficial effects of the present invention are:
1)建立以分布式并行处理方式为架构的柔性直流输电系统阀基控制体系架构，具有资源共享式网络通信协商机制保证系统信息传输的实时性和可靠性；并行计算协作求解使最优化方法和决策过程提高效率，分布式协调调度增加系统的可容错性和鲁棒性的优点，极大的提高处理能力，使复杂算法策略的实现在高电压大容量柔性直流输电系统中的应用得到保证；1) Establish a valve-based control architecture of flexible DC transmission system based on distributed parallel processing. It has a resource-sharing network communication negotiation mechanism to ensure the real-time and reliability of system information transmission; parallel computing collaborative solution makes the optimization method and The decision process improves efficiency, and the distributed coordinated scheduling increases the system's fault tolerance and robustness, greatly improves the processing capability, and ensures the application of complex algorithm strategies in high-voltage and large-capacity flexible DC transmission systems.
2)禁忌搜索优化算法灵活的记忆功能，灵活的存储结构和相应的禁忌准则避免重复搜索，并通过特赦准则赦免一些禁忌表中的优良状态，进而保证算法能够搜索到多极值点目标函数的全局最优解；2) tabu search optimization algorithm flexible memory function, flexible storage structure and corresponding tabu criteria to avoid repeated search, and exempt the excellent state in some taboo tables by special criteria, thus ensuring that the algorithm can search for multi-extreme point objective function Global optimal solution;
3)MMC技术电压平衡算法评判指标的确立，使柔性直流输电系统的子模块电容电压平衡确立了行之有效的判断标准，对各种策略算法的优劣可以系统全面的进行评价；3) The establishment of the evaluation index of the MMC technology voltage balance algorithm, the sub-module capacitor voltage balance of the flexible HVDC transmission system has established an effective judgment standard, and the merits of various strategy algorithms can be systematically evaluated comprehensively;
4)该算法所进行的试验验证手段，以仿真方式和动态模拟试验方式共同作为验证算法的方式，是高压大容量柔性直流输电的阀基控制技术所有算法全面系统的测试方法。4) The experimental verification method carried out by the algorithm is a method of verifying the algorithm together with the simulation mode and the dynamic simulation test mode. It is a comprehensive system test method for all the algorithms of the valve-based control technology of high-voltage and large-capacity flexible direct current transmission.
附图说明DRAWINGS
图1是本发明提供的模块化多电平换流器的拓扑结构图；1 is a topological structural view of a modular multilevel converter provided by the present invention;
图2是本发明提供的模块化多电平换流器子模块的拓扑结构图；2 is a topological structural diagram of a modular multilevel converter submodule provided by the present invention;
图3是本发明提供的子模块电容电压波动范围波形图；3 is a waveform diagram of a capacitor voltage fluctuation range of a sub-module provided by the present invention;
图4是本发明提供的子模块电容电压平衡优化的禁忌搜索优化算法流程图；4 is a flow chart of a tabu search optimization algorithm for sub-module capacitor voltage balance optimization provided by the present invention;
图5是本发明提供的仿真电路结构示意图；5 is a schematic structural diagram of a simulation circuit provided by the present invention;
图6是最近电平调制法的阀基控制系统动模平台试验交流波形图；6 is a waveform diagram of a test mode of a valve base control system of a recent level modulation method;
图7是最近电平调制法的阀基控制系统部分子模块电压波形图；7 is a voltage waveform diagram of a partial sub-module of a valve-based control system of a recent level modulation method;
图8是最近电平调制法的阀基控制系统单个开关的频率波形图；Figure 8 is a frequency waveform diagram of a single switch of a valve-based control system of a recent level modulation method;
图9是本发明提供的基于禁忌搜索优化算法的阀基控制系统动模平台试验交流波形图；9 is a schematic diagram of a test AC waveform of a valve-based control system based on the tabu search optimization algorithm provided by the present invention;
图10是本发明提供的基于禁忌搜索优化算法的阀基控制系统部分子模块电压波形图；10 is a voltage waveform diagram of a partial sub-module of a valve-based control system based on the tabu search optimization algorithm provided by the present invention;
图11是本发明提供的基于禁忌搜索优化算法的阀基控制系统单个开关的频率波形图；11 is a frequency waveform diagram of a single switch of a valve-based control system based on the tabu search optimization algorithm provided by the present invention;
图12是本发明提供的模块化多电平换流器的子模块电容电压平衡优化方法的流程图。12 is a flow chart of a sub-module capacitor voltage balance optimization method of a modular multi-level converter provided by the present invention.
具体实施方式detailed description
下面结合附图对本发明的具体实施方式作进一步的详细说明。The specific embodiments of the present invention are further described in detail below with reference to the accompanying drawings.
本发明提供一种模块化多电平换流器的子模块电容电压平衡优化方法，该方法用的系统为所述模块化多电平换流系统，采用模块化多电平换流器实现，模块化多电平换流器由三相六个桥臂构成，每个桥臂由子模块级联组成；所述子模块包括绝缘栅双极型功率管IGBT1和IGBT2、晶闸管V、储能电容C、真空开关、 电阻R1和电阻R2；所述电阻R1和电阻R2串联，组成R1-R2支路；所述真空开关、晶闸管V和IGBT2依次并联；所述IGBT1和IGBT2为上下结构且IGBT1的发射极连接IGBT2的集电极；所述IGBT1、R1-R2支路和储能电容C依次并联；本发明提供的模块化多电平换流器的拓扑结构图如图1所示。The invention provides a sub-module capacitor voltage balance optimization method for a modular multi-level converter, wherein the system uses the modular multi-level commutation system and is implemented by a modular multi-level converter. The modular multilevel converter consists of three phases of six bridge arms, each of which is composed of sub-modules cascaded; the sub-modules include insulated gate bipolar power transistors IGBT1 and IGBT2, thyristor V, and storage capacitor C , vacuum switch, a resistor R1 and a resistor R2; the resistor R1 and the resistor R2 are connected in series to form a R1-R2 branch; the vacuum switch, the thyristor V and the IGBT 2 are connected in parallel; the IGBT1 and the IGBT2 are upper and lower structures and the emitter of the IGBT1 is connected to the IGBT2 Collector; the IGBT1, R1-R2 branch and the storage capacitor C are sequentially connected in parallel; the topology structure diagram of the modular multilevel converter provided by the present invention is shown in FIG.
每个子模块包括上下两个全控型电力电子器件IGBT1和IGBT2、储能电容C和一个起到过流保护功能的晶闸管V，同时还有一个真空开关可以在子模块发生严重故障时通过闭合将该子模块从主回路中旁路；通过控制每个子模块内部IGBT的通断可以控制子模块输出电容电压(投入)或不输出电压(退出)，使每一相上下桥臂始终投入一定数量的子模块可以得到所需的直流侧电压，同时，通过调节上下桥臂各投入的子模块数量可以得到换流器的交流输出电压。子模块的拓扑结构图如图2所示。Each sub-module includes two upper and lower full-control power electronic devices IGBT1 and IGBT2, a storage capacitor C and a thyristor V that functions as an overcurrent protection function, and a vacuum switch that can be closed by a serious failure of the sub-module. The sub-module is bypassed from the main circuit; the sub-module output capacitor voltage (input) or non-output voltage (exit) can be controlled by controlling the on-off of the internal IGBT of each sub-module, so that each phase of the upper and lower bridge arms always inputs a certain amount. The sub-module can obtain the required DC-side voltage, and at the same time, the AC output voltage of the inverter can be obtained by adjusting the number of sub-modules input by the upper and lower arms. The topology diagram of the submodule is shown in Figure 2.
本发明提供的模块化多电平换流器的子模块电容电压平衡优化方法，其流程图如图12所示，包括下述步骤：The sub-module capacitor voltage balance optimization method of the modular multi-level converter provided by the present invention has a flow chart as shown in FIG. 12, and includes the following steps:
(1)确定子模块电容电压平衡控制的控制目标；(1) determining a control target of the sub-module capacitance voltage balance control;
子模块电容电压平衡控制的控制目标，包括以下几个方面：The control target of the sub-module capacitor voltage balance control includes the following aspects:
1)电容总体波动系数δ：为总体控制目标。系统运行过程中，每个子模块电容电压波动系数符合设计要求，此性能与系统传输功率、冗余子模块数量、电容容值、换流控制算法、均压策略等多种因素相关，是系统的综合控制目标。1) Capacitor overall fluctuation coefficient δ: is the overall control target. During the operation of the system, the capacitance voltage fluctuation coefficient of each sub-module meets the design requirements. This performance is related to various factors such as system transmission power, number of redundant sub-modules, capacitance value, commutation control algorithm, and voltage equalization strategy. Comprehensive control objectives.
2)电容不平衡度ε：为电容电压平衡的直接控制目标。系统运行过程中，同一时刻下每个桥臂内子模块电容电压均衡保持一致，这是电容电压平衡控制的直接目标。如图3所示；2) Capacitance unbalance ε: a direct control target for capacitor voltage balance. During the system operation, the capacitor voltage balance of each sub-module in each bridge arm is consistent at the same time, which is the direct target of the capacitor voltage balance control. As shown in Figure 3;
子模块电容电压在满功率传输情况下存在±8％的波动，考虑到直流电压波动、设备制造公差、测量误差、控制误差、电容电压平衡控制误差等因素，极限波动系数为±15％。The sub-module capacitor voltage has ±8% fluctuation under full power transmission. The limit fluctuation coefficient is ±15% considering factors such as DC voltage fluctuation, equipment manufacturing tolerance, measurement error, control error, and capacitor voltage balance control error.
电容不平衡度ε用下述表达式表示：The capacitance imbalance ε is expressed by the following expression:
Figure PCTCN2014091351-appb-000008
     式1>；
Figure PCTCN2014091351-appb-000008
 Formula 1>;
其中，
Figure PCTCN2014091351-appb-000009
使子模块电容电压在Umax和Umin范围内波动。among them,
Figure PCTCN2014091351-appb-000009
The sub-module capacitor voltage fluctuates within the range of Umax and Umin.
3)器件的开关频率：阻碍VSC-HVDC技术发展的重要障碍是换流器的损耗较大，降低电力电子器件开关频率能够大大降低换流器损耗；器件的开关频率较高，子模块投切较频繁，则会造成较大的开关损耗，因此，器件的开关频率是电压平衡算法的重要评判指标；3) Switching frequency of the device: The important obstacle to the development of VSC-HVDC technology is the large loss of the converter. Lowering the switching frequency of the power electronic device can greatly reduce the converter loss; the switching frequency of the device is higher, and the sub-module is switched. More frequent, it will cause a large switching loss, therefore, the switching frequency of the device is an important evaluation index of the voltage balancing algorithm;
4)平衡优化算法的实现难易：算法实现的难易程度与体系架构、硬件处理能力以及软件复杂度有关，也需要作为电压平衡算法的评判指标。4) The realization of the balance optimization algorithm is difficult: the difficulty level of the algorithm implementation is related to the architecture, hardware processing capability and software complexity, and also needs to be used as the evaluation index of the voltage balance algorithm.
(2)结合高压大容量柔性直流输电阀基控制技术需求、禁忌搜索优化算法特点以及分布式并行计算处理架构特点等，建立适用于高压大容量柔性直流输电 阀基控制的子模块电容电压平衡策略模型。建立子模块状态决策优化模型包括下述步骤：(2) Combining the requirements of high-voltage and large-capacity flexible DC transmission valve control technology, the characteristics of tabu search optimization algorithm and the characteristics of distributed parallel computing processing architecture, establish a suitable high-voltage and large-capacity flexible DC transmission. Valve-based controlled sub-module capacitor voltage balance strategy model. Establishing a submodule state decision optimization model includes the following steps:
<1>建立五元组；建立基于禁忌搜索优化算法的子模块状态决策优化模型的关键是目标函数的确定，子模块及整个系统的五个关键信息构成的五元组是目标函数的基础，所述五元组用下述表达式表示：<1> Establishing a quintuple; establishing the sub-module state decision-making optimization model based on the tabu search optimization algorithm is the determination of the objective function, and the quintuple composed of the sub-module and the five key information of the whole system is the basis of the objective function. The quintuple is represented by the following expression:
B＝{Ui；ib；tk；KSM；W}     式2>；B={U i ; i b ; t k ; K SM ; W} Equation 2>;
其中，Ui；ib；tk；KSM；W为子模块及换流器的五个关键信息，分别为：Ui为子模块电压大小，ib为桥臂电流大小及方向信息，tk为子模块开关动作时标，KSM为子模块信息状态，W为桥臂总能量；Among them, U i ; i b ; t k ; K SM ; W is the five key information of the sub-module and the inverter, respectively: U i is the sub-module voltage magnitude, i b is the bridge arm current magnitude and direction information, t k is the sub-module switch action time scale, K SM is the sub-module information state, and W is the total energy of the bridge arm;
<2>确定目标函数和约束条件：<2> Determine the objective function and constraints:
目标函数用下述表达式表示：The objective function is represented by the following expression:
Figure PCTCN2014091351-appb-000010
     式3>；
Figure PCTCN2014091351-appb-000010
 Equation 3>;
其中：α1，α2均为权重系数；η为子模块投切代价；φ为能量波动率；β为子模块信息状态；Where: α 1 , α 2 are weight coefficients; η is the sub-module switching cost; φ is the energy volatility; β is the sub-module information state;
子模块信息状态β表示为：The submodule information state β is expressed as:
Figure PCTCN2014091351-appb-000011
Figure PCTCN2014091351-appb-000011
子模块投切代价η由以下两部分组成：The submodule switching cost η consists of the following two parts:
Figure PCTCN2014091351-appb-000012
     式5>；
Figure PCTCN2014091351-appb-000012
 Equation 5>;
其中，γ1，γ2均为权重系数；Uave表示子模块电容电压平均值；Where γ 1 , γ 2 are weight coefficients; U ave represents the average value of the sub-module capacitance voltage;
能量波动率φ由下式表示，The energy fluctuation rate φ is expressed by the following formula.
     式6>； Equation 6>;
其中，ci和ui分别为各子模块电容和电压；i＝1,2,…n；n表示子模块个数； CN表示桥臂整个电容的电容值，UN表示整个桥臂的电压值；Where c i and u i are the capacitance and voltage of each sub-module respectively; i=1, 2,...n; n represents the number of sub-modules; C N represents the capacitance value of the entire capacitor of the bridge arm, and U N represents the entire bridge arm Voltage value;
子模块状态决策优化模型的约束条件包括：The constraints of the submodule state decision optimization model include:
A、总电压约束：Umin＜Σu＜Umax，总体电压不能超过上限和下限；A, the total voltage constraint: U min < Σ u < U max , the overall voltage can not exceed the upper and lower limits;
B、子模块电压畸变约束：
Figure PCTCN2014091351-appb-000014
子模块电压畸B, sub-module voltage distortion constraints:
Figure PCTCN2014091351-appb-000014
Submodule voltage distortion
变率小于上限值；The variability is less than the upper limit;
C、电气极限约束：过电流控制，用于保证桥臂电流值在允许限值内；桥臂电流值根据直流系统容量确定，1000WM，±320kV直流系统电流值在1600A±10％范围内；C. Electrical limit constraint: Overcurrent control is used to ensure that the bridge arm current value is within the allowable limit; the bridge arm current value is determined according to the DC system capacity, 1000WM, ±320kV DC system current value is in the range of 1600A ± 10%;
D、控制约束：子模块在单控制周期内不进行重复投切。D. Control constraint: The sub-module does not perform repeated switching within a single control cycle.
<3>确定禁忌表：<3> Determine the taboo table:
禁忌搜索到的每一个新状态都是当前点在其领域的移动操作产生的。因此移动和领域设计非常关键，模型采用领域解由集中性解和分散解组成的方法，这种方法通过子模块关键信息——子模块电压大小、桥臂电流方向、开关动作时标、子模块信息状态以及总能量组成的五元组产生的目标值进行精确的左右移动的同时，还在此五元组所在环随机产生新解，这个解就是所说的分散解。终止判据采用最优解连续爆出不变的最大迭代次数。Each new state that the taboo searches for is generated by the current point's movement operation in its field. Therefore, mobile and domain design is very critical. The model uses a domain solution consisting of a centralized solution and a decentralized solution. This method uses sub-module key information - sub-module voltage magnitude, bridge arm current direction, switching action time scale, sub-module The information state and the target value generated by the quintuple of the total energy are accurately moved left and right, and a new solution is randomly generated in the ring where the quintuple is located. This solution is the scatter solution. The termination criterion uses the optimal solution to continuously burst out the constant maximum number of iterations.
禁忌表是禁忌算法的关键所在，禁忌表中允许存在的最大移动数目称为禁忌表的规模。模型中禁忌表的规模采用子模块数目的开平方数乘以8，对禁忌表的更新采用传统的“先入先出”规则。之所以在搜索算法中出现释放准则是因为禁忌表有可能限制一些可以导致最好解的“移动”。模型建立采用基于适应值的“释放准则”：如果一个移动作用于当前解后，可达到一个到目前为止最优的适应值，则认为该移动满足了“释放准则”。The taboo table is the key to the taboo algorithm. The maximum number of movements allowed in the taboo table is called the size of the taboo table. The size of the taboo table in the model is multiplied by 8 in the square of the number of submodules, and the traditional “first in, first out” rule is used to update the taboo table. The reason why the release criterion appears in the search algorithm is because the taboo table may limit some "movements" that can lead to the best solution. The model is established using a "release criterion" based on the fitness value: if a movement is applied to the current solution and an optimum adaptation value is reached so far, the movement is considered to satisfy the "release criterion".
确定禁忌表包括下述步骤：Determining the taboo table includes the following steps:
a、通过分布式架构的信息共享协议机制将周期内各并行计算单元的子模块信息进行收集，形成五元组信息树进行保存，并计算其目标值；a. collecting the sub-module information of each parallel computing unit in the cycle through the information sharing protocol mechanism of the distributed architecture, forming a quintuple information tree for saving, and calculating the target value thereof;
b、根据目标函数、约束条件、控制保护单元和换流抑制单元确定的周期子模块投入数，并通过平衡优化算法对分布式并行计算系统中的计算单元的子模块信息目标值进行搜索，找到达到条件的一组局部最优解；b. According to the objective function, the constraint condition, the control protection unit and the commutation suppression unit, determine the number of periodic sub-module inputs, and search for the sub-module information target value of the computing unit in the distributed parallel computing system through the balance optimization algorithm, and find a set of local optimal solutions that meet the condition;
c、综合局部最优解：在其中搜索一组全局最优解，作为下一周期各时段进行投切的预投切子模块对象；c. Integrating a local optimal solution: searching for a set of global optimal solutions therein, as a pre-casting sub-module object for switching in each period of the next period;
d、确定每个预投切子模块的投切时间点和顺序，确保下一周期的子模块投切决策，将相关信息发送执行单元，相关信息指的是需要投切的子模块序号及系统的控制保护信息。d. Determine the switching time point and sequence of each pre-cast sub-module, ensure the sub-module switching decision of the next cycle, and send relevant information to the execution unit, and the related information refers to the sub-module serial number and system that need to be switched. Control protection information.
(3)对子模块电容电压进行平衡优化，本发明提供的子模块电容电压平衡优化的禁忌搜索优化算法流程图如图4所示，包括下述步骤： (3) Balancing and optimizing the sub-module capacitor voltage, the flow chart of the tabu search optimization algorithm for the sub-module capacitor voltage balance optimization provided by the present invention is shown in FIG. 4, and includes the following steps:
①读入系统参数(系统参数包括分布式系统运行参数和算法所需的参量和关键计算因子)，确定搜索的起始解(此为初始化的内容，即预设一个相对低值)；1 reading in the system parameters (system parameters include distributed system operating parameters and parameters required by the algorithm and key calculation factors), determine the initial solution of the search (this is the initial content, that is, preset a relatively low value);
②读入子模块五元组信息，形成初始化信息群；2 reading the sub-module quintuple information to form an initialization information group;
③确定禁忌长度，禁忌表长度，并将禁忌表置空；(禁忌长度是指需要搜索的信息数量，而禁忌表的长度则是搜索到的值的数量)3 Determine the length of the taboo, the length of the taboo table, and set the taboo table; (taboo length refers to the amount of information to be searched, and the length of the taboo table is the number of values searched)
④确定周期内需调整的时段：通过周期长度和预设精度来进行调整，即确定周期内投切子模块数目和投切间隔；4 determining the period to be adjusted within the period: adjusting by the period length and the preset precision, that is, determining the number of switching sub-modules and the switching interval in the period;
⑤生成当前解的领域：通过五元组的信息树，搜索相邻叶子和节点，生成解邻域；5 Generating the domain of the current solution: searching for adjacent leaves and nodes through the information tree of the quintuple to generate a solution neighborhood;
⑥从领域中选择目标函数最优的解，即候选解；6 Selecting the optimal solution of the objective function from the domain, ie the candidate solution;
⑦取适应度相对最优的候选解；7 taking a candidate solution with relatively optimal fitness;
⑧进行交叉操作，并判断选中解是否满足禁忌要求，若满足，则进行步骤⑨；否则将选中解从领域中删除，并返回步骤⑤；8 cross-operation, and determine whether the selected solution meets the taboo requirements, if yes, proceed to step 9; otherwise, the selected solution is deleted from the field, and returns to step 5;
⑨将选中的解作为新的当前解；9 will use the selected solution as the new current solution;
⑩判断是否超过最大迭代次数，若已达到，则得到最优解；否则，更新禁忌表，并对当前解进行适应度计算，返回步骤⑤。10 determines whether the maximum number of iterations is exceeded. If it has been reached, the optimal solution is obtained; otherwise, the taboo table is updated, and the fitness solution is calculated for the current solution, and the process returns to step 5.
(4)对子模块电容电压平衡优化进行验证：(4) Verify the sub-module capacitor voltage balance optimization:
为验证基于禁忌搜索优化算法的柔性直流系统阀基控制策略模型，通过PSCAD/EMTDC仿真软件和动态模拟试验装置，将最近电平逼近调制策略和禁忌搜索优化算法的阀基控制系统分别搭建系统模型；PSCAD/EMTDC仿真软件搭建极限参数单站三相无源逆变电路，如图5所示；动态模拟试验平台搭建极限参数的单相无源逆变试验；通过试验对比分析，得出禁忌搜索优化算法在评价指标上优于最近电平逼近调制策略，最近电平调制法的阀基控制系统动模平台试验交流波形及部分子模块电压波形和单个开关的频率波形如图6-8所示，基于禁忌搜索优化算法的阀基控制系统动模平台试验交流波形及部分子模块电压波形和单个开关的频率分别如图9-图11所示。试验结果对比分析汇总表如表1所示：In order to verify the valve-based control strategy model of the flexible DC system based on the tabu search optimization algorithm, the PSCAD/EMTDC simulation software and the dynamic simulation test device are used to build the system model of the valve-based control system of the nearest level approximation modulation strategy and the tabu search optimization algorithm. The PSCAD/EMTDC simulation software builds a single-site three-phase passive inverter circuit with limit parameters, as shown in Figure 5; the dynamic simulation test platform builds a single-phase passive inverter test with limit parameters; through the comparative analysis of the test, the tabu search is obtained. The optimization algorithm is superior to the nearest level approximation modulation strategy in the evaluation index. The valve-based control system of the current level modulation method and the voltage waveform of some sub-modules and the frequency waveform of a single switch are shown in Figure 6-8. The valve-based control system based on the tabu search optimization algorithm tests the AC waveform and the voltage waveform of some sub-modules and the frequency of a single switch as shown in Figure 9-11. The summary of the test results comparison table is shown in Table 1:
Figure PCTCN2014091351-appb-000015
Figure PCTCN2014091351-appb-000015
通过在线仿真和物理离线仿真试验结果表明，基于禁忌搜索优化算法实现的电压平衡策略的阀基控制系统，对比于最近电平逼近调制法，在高压大容量应用中，其平衡效果和性能都有不同程度的提升，加强了系统鲁棒性、容错性、稳定 性、可靠性以及可扩展性。The results of online simulation and physical off-line simulation show that the valve-based control system based on the tabu search optimization algorithm is compared with the recent level approximation modulation method. In high-voltage and large-capacity applications, the balance effect and performance are both Different degrees of improvement enhance system robustness, fault tolerance, and stability. Sex, reliability and scalability.
最后应当说明的是：以上实施例仅用以说明本发明的技术方案而非对其限制，尽管参照上述实施例对本发明进行了详细的说明，所属领域的普通技术人员应当理解：依然可以对本发明的具体实施方式进行修改或者等同替换，而未脱离本发明精神和范围的任何修改或者等同替换，其均应涵盖在本发明的权利要求范围当中。 Finally, it should be noted that the above embodiments are only for explaining the technical solutions of the present invention and are not limited thereto, although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that the present invention can still be The invention is to be construed as being limited by the scope of the appended claims.

Claims (9)

  1. 一种模块化多电平换流器的子模块电容电压平衡优化方法，所述方法用的系统为模块化多电平换流系统，建立以分布式并行处理方式为架构的柔性直流输电系统阀基控制体系架构，其特征在于，所述方法包括下述步骤：A sub-module capacitor voltage balance optimization method for a modular multi-level converter, the system for which is a modular multi-level commutation system, and a flexible DC transmission system valve constructed by distributed parallel processing A base control architecture, characterized in that the method comprises the following steps:
    (1)确定子模块电容电压平衡控制的控制目标；(1) determining a control target of the sub-module capacitance voltage balance control;
    (2)建立子模块状态决策优化模型；(2) Establish a sub-module state decision optimization model;
    (3)对子模块电容电压进行平衡优化；(3) Balance and optimize the capacitor voltage of the sub-module;
    (4)对子模块电容电压平衡优化进行验证。(4) Verify the sub-module capacitor voltage balance optimization.
  2. 如权利要求1所述的子模块电容电压平衡优化方法，其特征在于，所述步骤(1)中，子模块电容电压平衡控制的控制目标包括：The sub-module capacitor voltage balance optimization method according to claim 1, wherein in the step (1), the control target of the sub-module capacitor voltage balance control comprises:
    1)电容总体波动系数δ：为总体控制目标；1) The overall fluctuation coefficient of capacitance δ: the overall control target;
    2)电容不平衡度ε：为电容电压平衡的直接控制目标；2) Capacitance imbalance ε: a direct control target for capacitor voltage balance;
    3)器件的开关频率；3) the switching frequency of the device;
    4)平衡优化算法的实现难易。4) The implementation of the balance optimization algorithm is difficult.
  3. 如权利要求2所述的子模块电容电压平衡优化方法，其特征在于，所述电容不平衡度ε用下述表达式表示：The sub-module capacitor voltage balance optimization method according to claim 2, wherein the capacitance unbalance degree ε is expressed by the following expression:
    Figure PCTCN2014091351-appb-100001
       式1>；
    Figure PCTCN2014091351-appb-100001
     Formula 1>;
    其中，
    Figure PCTCN2014091351-appb-100002
    使子模块电容电压在U max和U min范围内波动。    among them,
    Figure PCTCN2014091351-appb-100002
    The submodule capacitor voltage is fluctuated within the range of U max and U min .
  4. 如权利要求1所述的子模块电容电压平衡优化方法，其特征在于，所述步骤(2)中，建立基于禁忌搜索的子模块状态决策优化模型包括下述步骤：The sub-module capacitor voltage balance optimization method according to claim 1, wherein in the step (2), establishing a sub-module state decision optimization model based on the tabu search comprises the following steps:
    <1>建立五元组；子模块及换流器的五个关键信息构成的五元组，所述五元组是子模块状态决策优化模型目标函数的基础，所述五元组用下述表达式表示：<1> Establishing a quintuple; a five-tuple composed of five key information of a sub-module and an inverter, the quintuple being the basis of an objective function of a sub-module state decision optimization model, wherein the quintuple is as follows The expression says:
    B＝{Ui；ib；tk；KSM；W}   式2>；B={U i ; i b ; t k ; K SM ; W} Equation 2>;
    其中，Ui；ib；tk；KSM；W为子模块及换流器的五个关键信息，分别为：Ui为子模块电压大小，ib为桥臂电流大小及方向信息，tk为子模块开关动作时标，KSM为子模块信息状态，W为桥臂总能量； Among them, U i ; i b ; t k ; K SM ; W is the five key information of the sub-module and the inverter, respectively: U i is the sub-module voltage magnitude, i b is the bridge arm current magnitude and direction information, t k is the sub-module switch action time scale, K SM is the sub-module information state, and W is the total energy of the bridge arm;
    <2>确定目标函数和约束条件；<2> Determine the objective function and constraints;
    <3>确定禁忌表。<3> Determine the taboo table.
  5. 如权利要求4所述的子模块电容电压平衡优化方法，其特征在于，所述子模块状态决策优化模型的目标函数用下述表达式表示：The sub-module capacitor voltage balance optimization method according to claim 4, wherein the objective function of the sub-module state decision optimization model is represented by the following expression:
    Figure PCTCN2014091351-appb-100003
       式3>；
    Figure PCTCN2014091351-appb-100003
     Equation 3>;
    其中：α1，α2均为权重系数；η为子模块投切代价；φ为能量波动率；β为子模块信息状态；Where: α 1 , α 2 are weight coefficients; η is the sub-module switching cost; φ is the energy volatility; β is the sub-module information state;
    子模块信息状态β表示为：The submodule information state β is expressed as:
    Figure PCTCN2014091351-appb-100004
       式4>；
    Figure PCTCN2014091351-appb-100004
    Equation 4>;
    子模块投切代价η由以下两部分组成：The submodule switching cost η consists of the following two parts:
    Figure PCTCN2014091351-appb-100005
       式5>；
    Figure PCTCN2014091351-appb-100005
     Equation 5>;
    其中，γ1，γ2均为权重系数；Uave表示子模块电容电压平均值；Where γ 1 , γ 2 are weight coefficients; U ave represents the average value of the sub-module capacitance voltage;
    能量波动率φ由下式表示，The energy fluctuation rate φ is expressed by the following formula.
    Figure PCTCN2014091351-appb-100006
       式6>；
    Figure PCTCN2014091351-appb-100006
     Equation 6>;
    其中，ci和ui分别为各子模块电容和电压；i＝1,2,…n；n表示子模块个数；CN表示桥臂整个电容的电容值，UN表示整个桥臂的电压值；Where c i and u i are the capacitance and voltage of each sub-module respectively; i=1, 2,...n; n represents the number of sub-modules; C N represents the capacitance value of the entire capacitor of the bridge arm, and U N represents the entire bridge arm Voltage value;
    子模块状态决策优化模型的约束条件包括：The constraints of the submodule state decision optimization model include:
    A、总电压约束：Umin＜Σu＜Umax，总体电压不能超过上限和下限；A, the total voltage constraint: U min < Σ u < U max , the overall voltage can not exceed the upper and lower limits;
    B、子模块电压畸变约束：
    Figure PCTCN2014091351-appb-100007
    子模块电压畸变率小于上限值；     B, sub-module voltage distortion constraints:
    Figure PCTCN2014091351-appb-100007
    The submodule voltage distortion rate is less than the upper limit value;
    C、电气极限约束：过电流控制，用于保证桥臂电流值在允许限值内；桥臂电流值根据直流系统容量确定，1000WM，±320kV直流系统电流值在1600A±10％范围内；C. Electrical limit constraint: Overcurrent control is used to ensure that the bridge arm current value is within the allowable limit; the bridge arm current value is determined according to the DC system capacity, 1000WM, ±320kV DC system current value is in the range of 1600A ± 10%;
    D、控制约束：子模块在单控制周期内不进行重复投切。D. Control constraint: The sub-module does not perform repeated switching within a single control cycle.
  6. 如权利要求4所述的子模块电容电压平衡优化方法，其特征在于，所述步骤<3>中，禁忌表包括禁忌表的规模，禁忌表的规模指的是允许存在的最大移动数目称，采用子模块数目的开平方数乘以8表示，对禁忌表的更新采用“先入先出”规则；The sub-module capacitor voltage balance optimization method according to claim 4, wherein in the step <3>, the taboo table includes the size of the taboo table, and the scale of the taboo table refers to the maximum number of movements allowed to exist, The number of squares of the number of submodules is multiplied by 8, and the "first in, first out" rule is used for the update of the taboo table;
    所述确定禁忌表包括下述步骤：The determining the taboo table includes the following steps:
    a、通过分布式架构的信息共享协议机制将周期内各并行计算单元的子模块信息进行收集，形成五元组信息树进行保存，并计算其目标值；a. collecting the sub-module information of each parallel computing unit in the cycle through the information sharing protocol mechanism of the distributed architecture, forming a quintuple information tree for saving, and calculating the target value thereof;
    b、根据目标函数、约束条件、控制保护单元和换流抑制单元确定的周期子模块投入数，并通过平衡优化算法对分布式并行计算系统中的计算单元子模块信息目标值进行搜索，找到达到条件的一组局部最优解；b. According to the objective function, the constraint condition, the control protection unit and the commutation suppression unit, determine the number of periodic sub-module inputs, and search for the target value of the calculation unit sub-module in the distributed parallel computing system through the balance optimization algorithm, and find the reach a set of local optimal solutions of conditions;
    c、综合局部最优解，在其中搜索一组全局最优解，作为下一周期各时段进行投切的预投切子模块对象；c. Integrating a local optimal solution, searching for a set of global optimal solutions therein, as a pre-casting sub-module object for switching in each period of the next period;
    d、确定每个预投切子模块的投切时间点和顺序，确保下一周期的子模块投切决策，将相关信息发送执行单元，相关信息指的是需要投切的子模块序号及系统的控制保护信息。d. Determine the switching time point and sequence of each pre-cast sub-module, ensure the sub-module switching decision of the next cycle, and send relevant information to the execution unit, and the related information refers to the sub-module serial number and system that need to be switched. Control protection information.
  7. 如权利要求1所述的子模块电容电压平衡优化方法，其特征在于，所述步骤(3)中，采用基于禁忌搜索的平衡优化算法对子模块电容电压进行平衡优化，包括下述步骤：The sub-module capacitor voltage balance optimization method according to claim 1, wherein in the step (3), the balance optimization algorithm based on the tabu search is used to balance and optimize the sub-module capacitor voltage, and the following steps are included:
    ①读入系统参数，确定搜索的起始解；1 read in the system parameters to determine the initial solution of the search;
    ②读入子模块五元组信息，形成初始化信息群；2 reading the sub-module quintuple information to form an initialization information group;
    ③确定禁忌长度，禁忌表长度，并将禁忌表置空；3 Determine the length of the taboo, the length of the taboo table, and set the taboo table blank;
    ④确定周期内需调整的时段：通过周期长度和预设精度来进行调整，即确定周期内投切子模块数目和投切间隔；4 determining the period to be adjusted within the period: adjusting by the period length and the preset precision, that is, determining the number of switching sub-modules and the switching interval in the period;
    ⑤生成当前解的领域：通过五元组的信息树，搜索相邻叶子和节点，生成解邻域； 5 Generating the domain of the current solution: searching for adjacent leaves and nodes through the information tree of the quintuple to generate a solution neighborhood;
    ⑥从领域中选择目标函数最优的解，即候选解；6 Selecting the optimal solution of the objective function from the domain, ie the candidate solution;
    ⑦取适应度相对最优的候选解；7 taking a candidate solution with relatively optimal fitness;
    ⑧进行交叉操作，并判断选中解是否满足禁忌要求，若满足，则进行步骤⑨；否则将选中解从领域中删除，并返回步骤⑤；8 cross-operation, and determine whether the selected solution meets the taboo requirements, if yes, proceed to step 9; otherwise, the selected solution is deleted from the field, and returns to step 5;
    ⑨将选中的解作为新的当前解；9 will use the selected solution as the new current solution;
    ⑩判断是否超过最大迭代次数，若已达到，则得到最优解；否则，更新禁忌表，并对当前解进行适应度计算，返回步骤⑤。10 determines whether the maximum number of iterations is exceeded. If it has been reached, the optimal solution is obtained; otherwise, the taboo table is updated, and the fitness solution is calculated for the current solution, and the process returns to step 5.
  8. 如权利要求1所述的子模块电容电压平衡优化方法，其特征在于，所述步骤①中，系统参数包括模块化多电平换流系统子模块的电流方向、调制投入切出子模块个数、子模块电压大小、子模块状态、子模块中IGBT器件开关频率、三相上下桥臂的电流、直流电压和桥臂电流变化率。The sub-module capacitor voltage balance optimization method according to claim 1, wherein in the step 1, the system parameter comprises a current direction of the modular multi-level commutation system sub-module, and the number of modulation input cut-out sub-modules Sub-module voltage size, sub-module status, IGBT device switching frequency in sub-module, current of three-phase upper and lower arms, DC voltage and bridge arm current rate of change.
  9. 如权利要求1所述的子模块电容电压平衡优化方法，其特征在于，所述步骤(4)中，采用在线仿真和物理离线仿真试验对子模块电容电压平衡优化进行验证。 The sub-module capacitor voltage balance optimization method according to claim 1, wherein in the step (4), the on-line simulation and the physical off-line simulation test are used to verify the sub-module capacitor voltage balance optimization.
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